1. Field of the Invention
The present invention relates to a vertical takeoff and landing (VTOL) aircraft, specifically to a vertical takeoff and landing aircraft consisting of core engines, turbofan engines consisting of a fan engine supported in biaxial support and supplied with high-pressure air from the core engine, and left/right front wings and left/right rear wings mounted with the fan engine on both left and right sides of both wings, wherein hovering and cruising are possible with the same propulsion units.
2. Description of the Related Art
Construction of airports near urban areas is desired to meet the demand for the movement between cities in a short time. However, it is difficult to construct an airport near urban areas because a long runway and vast air space are required for a conventional jet liner to make safe takeoff and landing. It is especially difficult for a small or medium size city, because the construction of an airport invalues large expense, and for a large city also it is difficult, because of the difficulty of securing a vast area, the problem of the high noise produced by jet liners, and safety problems. Therefore, even with a large city the airport is constructed to be remote from the city, and it is necessary for citizens dwelling in a small or medium size city to go to an airport located near an urban area, thus expending a lot of time. Accordingly, it is becoming expensive for citizens in small or medium size cities, and also for citizens in large cities, to access the airport, and there may occur the case where it saves more time and expense to travel overland than by air.
As a means to solve problems like this, it is conceivable to use a helicopter or vertical takeoff and landing (VTOL) aircraft. However, the weight carried by a helicopter is limited and its speed is also limited, so it is not a satisfying means for solving the problem mentioned above. On the other hand, a vertical takeoff and landing aircraft can cruise with high speed and does not need a long runway for taking off, because a VTOL aircraft takes off from the ground vertically, so that the area of the airport does not need to be large, resulting in low cost for the construction thereof, which will enable a small or medium size city to construct the airport, and also enabling a large city to construct the airport nearer to the urban area. Therefore, VTOL aircraft are suited for high-speed movement between cities.
As vertical takeoff and landing aircraft that have been put to practical use, there are a tilt-rotor type and a tilt-wing type. The tilt-rotor type vertical takeoff and landing aircraft has rotors (engines) each of which can be tilted together with its fan, and when taking off the rotors take a vertical position to takeoff vertically and when cruising the rotors take a horizontal position. The tilt-wing type has fans attached to the wings which can be tilted, and when taking off the wings are tilted to a vertical position, and when cruising the wings are allowed to be in a horizontal position.
The moment about the center of gravity of the aircraft (that means balancing) is important for vertical takeoff and landing aircraft. There has been proposed a type which provides exclusive fans on both sides of the airframe for attitude control, or a type which provides fans (thrust point) at the front and rear of the airframe to maintain balance.
However, the engines of the tilt-rotor type and tilt-wing type VTOL aircraft are large and they are necessarily mounted at positions apart from the center of gravity of the airframe, so that the moment of inertia becomes large, resulting in poor mobility. Further, in the case of the 2-fan type, the diameter of the fan is large, and a gliding landing is impossible. Therefore, in case of a fault in the tilting mechanism, landing is impossible, and at the same time, stable maneuverability cannot be ensured because of 2-point support. These are drawbacks of these types and induce safety problems. Particularly with the tilt-wing type, the size of the tilting mechanism has to be large and the attitude control mechanism (fans, etc. at the front and rear of the airframe) is complicated, which generally results in increased weight of the airframe. Therefore, there has been a concern whether a practical VTOL aircraft could be realized, or whether the payload would be decreased due to the increase in weight.
To solve the problems mentioned above, a VTOL aircraft of stable maneuverability, low noise level, and high cruising speed by using turbofan engines with separate core engines is proposed in Aviation Technology, published in July 2001, pp. 10˜19, under the title of “A Conception of an innovative VTOL Passenger aircraft” (hereafter referred to as prior art 1), and in Japanese Patent No. 1861368 (Japanese Patent Publication No. 5-87655, hereafter referred to as prior art 2).
A turbofan engine with separate core engine is an engine which consists of a core engine composed of a compressor, a combustor, and a turbine to drive said compressor, and a fan engine composed of a combustor, a turbine to drive the fan, and a fan driven by said turbine, high-pressure air being supplied from said core engine to the fan engine through high-pressure duct or the like, and the core engine and fan engine being located separately.
A conventional turbofan engine consists of a fan, a compressor, a combustor, and a turbine. These are disposed in a casing. The fan is connected with a shaft to the turbine. Part of the air accelerated by the fan is introduced to the compressor to be compressed thereby and the compressed air is introduced to the combustor to burn the fuel injected thereinto. The combustion gas is introduced to the turbine to drive the turbine, and the remaining air accelerated by the fan is ejected from the fan engine. Thus thrust is obtained by this ejected air and the exhaust gas ejected from the turbine of the fan engine. As the fan and turbine are located on the same axis, the core engine must be located along the direction of the fan and the mounting position of the turbofan engine to the aircraft is restricted, resulting in a low degree of design flexibility.
On the contrary, with a turbofan engine with a separate core engine, the core engine and fan engine can be located separately. In addition, the fan engine can be composed with a thin section, therefore the core engine is not influenced by the operation state of the fan engine and an engine which is superior in stability and quick in response can be obtained. The engine is easy to be developed, its maintainability is better, and further it is outstandingly increased in flexibility as a plurality of fan engines can be driven by one core engine.
For this reason, in the prior art 1 and 2, as shown in FIG. 15, turbofan engines with separate core engines are used. Core engines 160 are mounted in the rear part of fuselage 161, lift fans 162 for vertically taking off in a hovering state are provided on the left/right wings 163 at both sides of the fuselage 161, cruising fans 164 to be used when cruising are mounted at the rear of the fuselage 161, and the lift fans 162 and cruise fans 164 are selectively driven by the core engines by switching the operation of both fans. With a construction like this, a high-speed VTOL aircraft, of which there has been no practicability hitherto, can be realized.
That is, as the thickness of the lift fan 162 is thin, the noise from the lift fans can be lowered to a very low level, the airframe can be formed so that it is suited for cruising at high speed, and the aircraft is highly stable, being less influenced by the fluctuations or non-uniformity of air currents. Further, as the core engines 160 are common for the lift fans 162 located symmetrically with regard to the center of gravity of the airframe, the aircraft does not lend itself to being thrown off-balance by any irregularity in the core engines 160. As the cruise fans 164 and lift fans 162 share the use of the core engines 160, the weight of the airframe is reduced.
However, the VTOL aircraft of prior art 1 or 2 has separate fans for cruising and lifting as shown in FIG. 15, so during lifting, the weight of the cruise fans 164 is useless and excess weight, and when cruising, the weight of the lift fans 162 is useless and excess weight. Further, as the lift fans 162 are fixed to the fixed wings, fine adjustments in hovering are difficult.